Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail)

v3.19.1
Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail) - Employee Stock Options - $ / shares
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Risk-free interest rate 2.59% 2.68%
Expected term (in years) 6 years 29 days 6 years 7 days
Dividend yield 0.00% 0.00%
Volatility 109.00% 108.00%
Weighted-average fair value of stock options granted $ 3.93 $ 8.85